I thought I left a comment earlier for you. But I guess the internet gremlins ate it.

Oil pastel will never completely dry. It will set up and feel dry to the touch, usually over night. Different brands of oil pastels have different "drying" times. Of the artist grade pastels Sennelier seems to dry the slowest.

Oil pastels are not normally varnished for protection. Instead they are displayed under glass in a frame. There are products out there that are sprayed on for protection and Sennelier also make one for their product but in my opinion it hasn't been around long enough for me to trust it.

I've sketched on rocks, glass, cardboard etc. and have found very few thing that the OP won't stick to. I've experimented using them on cloth but not on anything that will be handled.

I am also very new to pastels. I took a class from one of 'the masters' a bit ago, and he claimed that using the fixative that you can use on graphite or charcoal darkened pastels colors and took out some of their vibrancy. He also said that pastel "binds to itself" as well as the paper, which is why pastels of great age still exist (and haven't ended up on someone's sleeve).

1. just frame under glass- no need to even mat it you dont want to. Mat if you want to. either way is fine. She does not use mats and puts the painting right up to the paper. She said to just make sure that the painting does not move against the glass. That is what can smear it.

2. fixative sprays dull the reflective quality of pastels- what makes them glow, so she does not use any fixative

3. she uses cheap normal glass. her argument is that most people who collect her art know not to put art in sunlight, so why spend $$ on the extra cost of no-glare glass.

I am new to pastels and am loving them! I love how I can make changes (coming from watercolors which are a one-shot deal!). They are much like oil painting.

The glass suggestion is good, but I would be concerned if the art is touching the glass. Maybe visit a museum and see how pastels are framed...

Oil pastels take a long time to dry. I found that they can be sprayed lightly with crystal clear, whether this yellows over time is questionable. Maybe do an experiment with a test piece. Otherwise just frame under glass.

Experiment on different surfaces, why not? just do not expect it to be archival unless the surface itself is archival to begin with.

I fear you received some bad advice concerning mounting the pastel directly against the glass. If you choose not to mat the finished work it can be framed by using spacers between the glass and painting.

With changes in temperature most materials expand and contract unfortunately not necessarily at the same rate. Also consider that moisture may form with changes in temperature and humidity.

Should the piece ever need to be re framed, for whatever reason, the result will probably be very sad experience.